The present invention concerns a treatment method which is used to form a lubricating coating film that is suitable for cold plastic working, i. e., wire drawing, tube drawing, forging or header working, etc., that is performed while the metal is cold, on the surface of ferriferous metals such as low-carbon steel, high-carbon steel and low-alloy steel, and the like. (Hereinafter, unless otherwise noted, the simple term "steel" is to be understood as encompassing all such materials, and the shorter phrase "cold working" implies "cold plastic working").
When steel is subjected to cold working, the surface to be worked, called the "workpiece", is provided with a lubrication treatment beforehand in order to reduce wear on at least one working tool surface, between which and the workpiece surface mechanical force is exerted during cold working to cause the desired deformation of the workpiece to be accomplished by the cold working, and to prevent sticking of the material being worked to the tools. If the degree of deformation of the workpiece to be accomplished by the cold working performed is relatively low, an oil, which may contain extreme-pressure additives and/or additives that improve the lubricative properties of the oil, may be satisfactorily used as the only lubrication treatment. In cases where a high degree of deformation of the workpiece is desired, a two-stage lubrication method is widely used. First a zinc phosphate type conversion treatment is formed on the workpiece surface by contacting it with a suitable zinc phosphating liquid composition containing (for example) nitrite as an oxidizing agent, with this treatment solution being heated to a temperature of 70 to 80.degree. C. After a conversion coating is thereby formed on the surface, the conversion coated surface is then contacted with a soluble metal soap solution whose main component is (for example) sodium stearate (e. g., PALUBE.RTM. 235 treatment manufactured by Nihon Parkerizing Co., Ltd.). During this contact, the stearate solution is heated to a temperature of 70 to 90.degree. C., so that a zinc stearate lubricating layer is formed on the surface of the zinc phosphate coating film and a sodium stearate layer is formed on top of this zinc stearate lubricating layer. Furthermore, research on improvement of the underlayer coating film has been conducted with the aim of improving the performance of such a lubrication treatment coating film. Some results of such research are disclosed in Japanese Patent Application Kokoku No. 60-20463. The conversion coating treatment used in the invention of this reference is performed at a temperature of approximately 80.degree. C., using a zinc-calcium phosphate type treatment solution with specified component concentrations.
When the two types of underlayer treatments using the above mentioned zinc phosphate type treatment solution and zinc-calcium phosphate type treatment solution are examined, it is found that both treatments require a high formation treatment temperature, and both result in the generation of large amounts of sludge in the treatment solution. In addition, the following problem also arises: Large amounts of nitrites are used as oxidizing agents, and since these nitrites break down in a concentrated acidic replenishing agent, they must be replenished from a separate replenishing tank.
The object of the present invention is to provide a lubrication treatment method for use in cold working of steel, which method includes an operation of forming a zinc or zinc-calcium phosphate conversion coating and makes it possible to achieve at least one of the following benefits compared with the prior art: to lower the temperature of the treatment solution, to reduce the amount of sludge, to improve the quality of the cold-worked underlayer beneath the coating film that is formed, and to make single-liquid type replenishment practical (because there is no decomposition in a concentrated acidic replenishment composition).